As optical fiber technology is being more broadly applied in the telecommunications, data communications and CATV industries, the fiber optic component industry is now confronted with increasing requirements for good performance and high reliability of fiber optic components. In particular, the optical components are required to maintain substantially constant performance characteristics and reliability under wide ranges of temperature variations. High humidity resistance is also required. Currently, most of in-line fiber optic components are designed and manufactured based on optical collimators which provide low-loss light transmission from the input fiber to the output fiber through an optical element. As a basic building block of the fiber optic components, the reliability and level of performance of the fiber optic components depend heavily on the reliability and the performance characteristics of the optical collimators. Dual fiber optical collimators are one type of collimators widely employed in making the fiber optic components. For example, the dual fiber optical collimators are employed to make thin film filter based wavelength division multiplexers and hybrid optical isolators.
FIG. 1A shows the structure of a typical dual fiber optical collimator that includes a dual fiber pigtail 30, a GRIN lens 15, a glass tube 40 and a stainless steel holder 50. In a typical manufacturing process, the relative position of the GRIN lens 15 to the fiber pigtail 30 is adjusted to achieve a lowest transmission loss from the input fiber 20 to output fiber 25. The GRIN lens 15 and the dual fiber pigtail 30 are fixed together by applying an ultraviolet (UV) curing epoxy 35. Then the fiber pigtail 30 is fixed to a glass tube 40 by applying an UV curing epoxy 45 and the glass tube 40 is fixed to a stainless steel holder 50 by a heat curing epoxy 55. The typical method and system provides the dual fiber optical collimators with fair performance and reliability suitable for some types of applications. However, the dual fiber optical collimators manufactured with the conventional processes often fail and perform poorly when they are implemented in fiber optic components that demand long term operation in a high temperature, e.g., 85.degree. C., and high humidity, e.g., 85% humidity, environment. The UV curing epoxy bonding, e.g., epoxy 35, is often broken when subject to such operation conditions and then optical signal transmission becomes very poor. Thus, further development and reliable fiber optic components with high level of performance is limited to these difficulties. In a pending patent, entitled {character pullout} Dual Fiber Optical Collimator{character pullout}, filed recently by the present inventor, improvements are achieved for the reliability of the dual fiber optical collimators. In the improved manufacturing process as shown by FIG. 1B, for the pending application, the GRIN lens 15 and the dual fiber pigtail 30 are first sealed by applying tiny amount of an ultraviolet (UV) curing epoxy 35. After the relative position of the GRIN lens 15 to the fiber pigtail 30 is adjusted to achieve a lowest transmission loss from the input fiber 20 to output fiber 25, the GRIN lens 15 and the fiber pigtail 30 are fixed together by applying a heat curing epoxy 40. Since heat-curing epoxy bonding is much stronger than UV curing epoxy bonding, the improved dual fiber optical collimators have much better reliability as compared to the typical ones. However, due to the use of sealing UV curing epoxy, the dual fiber optical collimators, even with improved reliability, still cannot fully meet the more stringent application requirements. The small quantity UV epoxy often causes reliability problems due to an observed characteristic that the performance of UV curing epoxy demonstrates too much temperature dependence. Further reliability concerns are caused by the fact that the UV curing epoxy has low humidity resistance. Thus, the improved dual fiber optical collimators can only prove a partial solution.
Therefore, a need still exists in the art of design and manufacturing of the dual fiber optical collimators to provide new material compositions, device structure, and manufacturing processes to overcome the difficulties discussed above. Specifically, a technique to provide the collimators without use of any UV curing epoxy is required. Since production costs have been an important factor prohibiting practical implementation of fiber optical technology, it is also highly desirable that the cost of such technology would be as low as possible.